This quest was given by an NPC found standing around the Canyon Rim Mines. Despite the quest's title, the NPC did not resemble the Diablo 2 Necromancer, and did not use any Necromancer powers. It's possible the title was chosen simply to work as a sort of Easter Egg for fans playing the Blizzcon demo.

When found, the old man (who was shirtless and heavily-bearded), explained that he was attempting to exorcise the spirits of some soldiers that had died in the surrounding ruins, but that they were too strong for him. He requested assistance from the player.

Click it!

To assist him, players searched the immediate area and found three glowing altars, as seen in the screenshot. When an altar was activated (by clicking on it) a pack of monsters was summoned. This happened on all three altars, and after clearing them all out, players returned to the old man. One final ambush occurred then, and after defeating the last bunch of monsters the NPC provided the player with a reward of experience and an item.